The Victorian Government and Transurban understand that air quality is an important issue for residents of Melbourne’s inner west, with many concerned about emissions from trucks travelling through the local area.

With thousands of tunnels in the world, there are well-established and effective processes to manage emissions. Experience from previous motorway tunnel projects, both in Australia and around the world, tells us that emissions from well-designed tunnel ventilation structures do not measurably affect local or regional air quality. This is backed up by scientific research.

Air pollution is caused by a number of factors, such as emissions from motor vehicles, industry, domestic sources and natural sources. One of the biggest contributors to air pollution in Melbourne is emissions from motor vehicles, although this has improved in recent years. Air quality is expected to further improve as new vehicles with improved technology are entering the vehicle fleet faster than the rate of traffic growth (Source: Environment Protection Authority Victoria – Future air quality in Victoria – Final Report).

Meet Bruce, our air quality expert.

Video transcript Western Distributor – air quality (DOCX 14kb)

What we've heard so far

Through consultation earlier this year, some of the feedback received included:

  • the local community see a great benefit of the project will be improved air quality, achieved by reducing the number of trucks on local roads
  • there is a desire to show predicted changes to air quality achieved by this project
  • locals are seeking assurances that trucks will use the new road connections and/or propose additional truck bans be implemented to reduce toll avoidance
  • concern about location of tunnel entry and exit points, and ventilation structures
  • air quality is an existing issue, in some locations, with concern about health implications
  • there is a desire to see international best practice applied to the design of a tunnel ventilation system
  • the community would like certainty about the location of ventilation structures.

Air quality monitoring and modelling

The project team will use scientifically validated and extensively used atmospheric dispersion models to predict impacts associated with ventilation structure emissions, and this will be publicly reported.

Experience from previous motorway tunnel projects, both in Australia and around the world, tells us that air dispersion modelling for tunnel ventilation structures is robust and a conservative prediction.

Data from Environment Protection Authority Victoria’s (EPA) Footscray Ambient Air Quality Monitoring Station will be used to assess existing air quality in the project area. The Footscray Station provides a robust dataset of historical and current air quality data which is also published on the EPA Victoria website.

We’re putting in place a range of approaches to ensure that the air quality assessment is comprehensive and the health impacts of the project are considered, including:

  • assessing existing conditions to inform analysis of the potential change in air quality
  • assessing a range of pollutants including PM10 and PM2.5
  • supplementing the air quality assessment with a program of local air quality monitoring at five locations in the inner west
  • considering impacts on air quality in all areas within 1km of the tunnel ventilation structures
  • conducting the first Victorian health impact assessment for a major road project
  • using internationally-recognised air dispersion modelling to help inform the design of a safe and effective ventilation system
  • measuring air quality for at least one year before the tunnels open and after operations commence
  • make all air quality monitoring results publicly available.

For more information on air quality monitoring visit the Project Investigations page.

Air quality standards

Victorian air quality standards are established in State environment protection policies (which are derived from national standards), which include objectives for pollutants associated with motor vehicle emissions such as carbon monoxide (CO), nitrogen dioxide (NO2) and particles (PM10 and PM2.5).

In early 2016, the National Environment Protection (Ambient Air Quality) Measure (NEPM) was varied to include new reporting standards for annual average and 24-hour PM2.5 particle levels with further movement of these standards by 2025. The NEPM was also varied to establish an annual average standard for PM10 particles. Victoria has indicated it will set a more stringent annual average PM10 standard.

What do these terms mean?

Particulate Matter (PM) is the term for particles found in the air, including dust, dirt, soot, smoke and liquid droplets. Particles result from all sorts of combustion. They are emitted from industrial processes, motor vehicles and domestic fuel burning as well as from bush fires.

A Micron equals 1 millionth of a metre – a strand of human hair is approximately 100 microns thick.

PM10 is coarse particulate matter that is less than 10 microns in diameter.

PM2.5 is fine particulate matter that is less than 2.5 microns in diameter.

Nitrogen dioxide comes from the combustion of fossil fuels, such as petrol, diesel, coal and gas.

Carbon monoxide comes from the burning of fuels that contain carbon, such as petrol, gas, oil and coal. Sources include motor vehicles, boilers, heaters and industrial equipment.

Managing tunnel air quality

All tunnels need a ventilation system to move air into, through and out of the tunnel in a safe and efficient way. A typical ventilation system includes:

  • jet fans to control air movement through the tunnel
  • ventilation fans at the exits to push air up and into the ventilation structures
  • ventilation outlets to discharge air.

These systems are designed to meet stringent in-tunnel and local air quality criteria. The Victorian air quality standards (consistent with national standards) set the levels and ongoing monitoring is done to check that tunnel operators meet air quality requirements for the tunnels. These requirements and regular measurements will be publicly available.


There is well-proven methodology from all over the world for designing tunnels and their ventilation systems. Primarily these systems rely on the effective movement of fresh air through the tunnel to maintain in-tunnel air quality and well-designed ventilation structures to provide for effective dispersion of emissions.

In some cases, tunnels have a filtering system, which is primarily used where local conditions need an improvement in visibility by recycling air within the tunnel.

A number of considerations, including the net environmental effect of such systems and air dispersion modelling, will help inform the design of a ventilation system.

Design of ventilation structures

Well-designed ventilation outlets keep the air inside and outside the tunnel safe at all times – protecting the health and safety of local residents and people driving through the tunnels.

Ventilation structures have been designed countless times in Australia and overseas, and we know that ventilation structures work best when located near the tunnel exits. A number of other factors also need to be considered when identifying suitable locations, including; air dispersion modelling results, potential sensitive receptors, available land and input from local communities.

Illustration showing the typical air flow in a tunnel

Typical air flow in a tunnel with fresh air flowing in at each end, air being pushed by vehicles in the tunnel and air exiting via the ventilation shaft.

Environment Effects Statement

A technical assessment of air quality will be undertaken and released in the Environment Effects Statement (EES) that is being prepared for the Western Distributor project and the application for Works Approval to EPA Victoria.

The assessment will include an overview of the existing conditions and an analysis of potential changes in air quality. Air dispersion modelling will help inform the design of a safe and effective ventilation system. The model will consider factors such as current air quality, trafficmvolumes, type of vehicles and tunnel design.

The EES will be publicly exhibited in early 2017. Community and stakeholder submissions will be considered by an independent planning panel and submitters will have the opportunity to present to the planning panel.

After considering community and stakeholder submissions, the panel will make recommendations to the Minister for Planning about controls on how the project is constructed and operated.

Download the Air quality discussion paper (PDF 552kb)

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